This invention relates to improved material haulage vehicles and, more particularly, to low-height mine-haulage vehicles of the type commonly known as "shuttle cars" used for hauling loose materials in underground trackless mines.
Shuttle cars have to carry heavy loads through low height, closely confined mine passageways with rough, uneven floors. Cars commonly used have a loading end with a pair of undriven steering wheels and a pair of driven wheels coupled in articulating relation to a discharge end also providing a pair of undriven steering wheels. The undriven steering wheels of the discharge end are coupled by a steering mechanism to the steering wheels of the loading end such that turning the steering wheels of the discharge end will result in an equal and opposite rotation of the steering wheels of the loading end.
Specific cars in common use are known as 18-SC shuttle cars manufactured and sold by Joy Manufacturing Company of Pittsburgh, Pennsylvania.
The structure of such cars is identified with U.S. Pat. Nos. 2,426,960; 2,590,300; 2,654,547; 2,777,526; 2,962,176; 2,472,048; 2,593,643; 2,654,548; 2,777,530; 2,970,664; 2,543,519; 2,654,382; 2,598,104, 2,913,964; 3,008,592; 2,589,235; 2,654,383; and 2,858,897 and U.S. Pat. No. Re. 24,178, each incorporated herein by reference.
While adaptive to many mining situations, where the mine surface is wet and uneven, the cars have experienced serious haulage problems. At times, the problem has become so acute that the cars could not be used, and the only coal produced was by using a scoop.
A need, therefore, exists for a car providing better traction on wet, uneven surfaces to alleviate the problems presently encountered with six wheel cars, providing a pair of driven wheels and two pair of undriven steering wheels.